The present invention relates to a new and distinct cultivar of Sedum and given the cultivar name of ‘Thunderhead’. Sedum is in the family Crassulaceae. Sedum ‘Thunderhead’ originated from a planned breeding program to produce hybrids with dark leaves, short stems and large inflorescences. Sedum ‘Thunderhead’ originated from a cross between an unnamed, proprietary, an unpatented Sedum telephium 2-5 as the seed parent and Sedum spectabile ‘Neon’, unpatented, as the pollen parent.
Compared to the seed parent Sedum telephium 2-5, the new cultivar is has much larger inflorescences with better flower color, and larger, lighter colored leaves.
Compared to the pollen parent, Sedum spectabile ‘Neon’, the new cultivar, has leaves that are a dusky gray green color rather than yellow green.
Compared to Sedum ‘Class Act’ (U.S. Plant Pat. No. 20,125), the new variety is taller with leaves that dark rather than green with dark margins. The flowers of the new variety are smaller in larger, denser, and flatter inflorescences. The flowers of the new variety are more purple in color.
Compared to Sedum ‘Beach Party’, (U.S. Plant Pat. No. 22,810), the new variety is larger in habit, and has darker leaves and flowers.
This new and unique Sedum is distinguished by:                1. medium deep red purple flowers in very large inflorescences,        2. dusky, dark leaves,        3. strong, upright stems, and        4. a medium, clumping habit.        
This new cultivar has been reproduced only by asexual propagation (division and tissue culture). Each of the progeny exhibits identical characteristics to the original plant. Asexual propagation by division and tissue culture using standard micropropagation techniques with terminal and lateral shoots, as done in Canby, Oreg., shows that the foregoing characteristics and distinctions come true to form and are established and transmitted through succeeding propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may vary with variations in environment without a change in the genotype of the plant.